In a hydroelectric power plant, a penstock is ordinarily provided for introducing a great quantity of pressurized water into the power plant, and the flow of the pressurized water is controlled by the open-and-closing operation of the guide vanes.
In this case, the open-or-closing speed of the guide vanes must be selected extremely carefully, and when the speed is too fast unallowable high or low pressure is created in the penstock due to a water hammering effect. Thus, in the case of a comparatively long penstock, the open-or-closing speed of the guide vanes is made considerably slow. However, such a slow operation of the guide vanes is not advantageous for the governor control of the water turbine, and there exists a possibility of causing unstable operation of the governor or an excessive speed-rise in rotation of the water-turbine.
For overcoming the above described difficulty, a pressure regulator has been provided in the power plant, which quickly opens when the guide vanes are to be closed at a high speed and then gradually closes under the action of a dash-pot. However, the pressure regulator is kept closed when the guide vanes are being opened.
However, the pressure regulator of the conventional arrangement is not free from the possibility of being inoperative at the time the guide vanes are being closed at a high speed due to trouble occurring in the dash-pot or in a pressurized fluid distrubuting valve for the pressure regulator. This necessitates that the penstock must be designed in consideration of the possibility of being subjected to a high-pressure caused by the inoperation of the pressure regulator, and the merit of providing the pressure regulator is greatly reduced.
For eliminating the above described drawbacks of the known arrangement, there has been made a proposal wherein an auxiliary servomotor having a capacity substantially equal to that of the guide-vane servomotor is further provided for the pressure regulator, the auxiliary servomotor and the guide-vane servomotor being connected through pipe lines, and in the normal operation of the water turbine, the guide vanes are open-or-closed at a slow speed while the pressure regulator is completely closed. But in the case when the guide vanes are required to be closed at a high speed, the pressure regulator is quickly opened, the quick opening of the pressure regulator is transferred to the guide-vane servomotor through the auxiliary servomotor and the pipe lines, so that the guide vanes are closed at a high speed.
According to this proposal, however, the water turbine must always be operated in a load-limiting state, thereby sacrificing the speed-regulating function of the governor. Such features are of course not desirable in the operation of an electrical power network, and the fully loaded operation of the individual power plant is thereby made impossible.
In order to eliminate the above described drawbacks of the known arrangement, there has been a proposal wherein an auxiliary servomotor having a capacity substantially equal to that of a servomotor for guide vanes is used for a pressure regulator the auxiliary servomotor and the servomotor for the guide vanes being connected to each other through pipes lines, wherein the pressure regulator is controlled by the positions of an auxiliary servomotor for the governor and the servomotor for the guide vanes which are otherwise controlled by the difference between the opening position of the pressure regulator and the set position of a load limiter for the water turbine whereby, at the time of free running of the water turbine utilizing the governor, the guide vanes are operated in response to the open-and-closing operation of the pressure regulator thereby to suppress any variation in the water flowing speed in a penstock and at the time of the load-limiting operation of the water turbine the pressure regulator is fully-closed for minimizing ineffective flow of water.
According to this proposal (e.g. U.S. Pat. No. 3,891,999), however, at the time of free running of the water turbine utilizing the governor, the guide vanes must be operated by the distributing valve for the pressure regulator through the pressure regulator, the auxiliary servomotor for the pressure regulator and pipe lines connecting the auxiliary servomotor for the pressure regulator and the guide vane servomotor, thereby sacrificing sensibility of the movement of the guide vanes and hence the stability of the water turbine operation.